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Friday, October 9, 2015

Much surprise is exhibited by people when they realize that the no-go area around Chernobyl is turning into a wild life sanctuary. We see such comments as "People are worse than nuclear fall out", referring to the ever increasing richness and abundance of the flora and fauna in the area since people were excluded. No argument there but it misses the basic biological point.

It is, of course true that if you are exposed to sufficient radiation, such as you might find inside one of the damaged Fukushima reactors and you stay in there long enough (not all that long), you will have your insides sun tanned and you will die. Expressing it a bit more scientifically, the ionizing radiation wizzing through your body will disrupt so much of your physiology that your organism will cease to work.

Less radiation than a fatal dose will cause an increase in mutations in your germ cells (sperm or eggs) and as we all know, most mutations decrease the fitness of your offspring to survive in their environment. The effect on an individual germ cell, being hit with increased radiation is something of a lottery. One individual from a given germ cell may be made less fit, another not effected. A very very small proportion will have a mutation that will be advantageous. And remember that we all live with a background level of radiation. We get it from the sky as cosmic rays (heavy nuclei traveling at near relativistic speeds) and from radioactive elements in our soil. To some extent our genetics is adapted to this radiation and there are mechanisms in our bodies that repair at least a portion of the copying errors.

Let's jump sideways for a moment. Think of a pair of wolves. The mother can easily have three pups (often many more) each year and a wolf can easily live for 10 years. Let's say 30 pups born to the couple over their life time. Why are we not overrun by wolves. A sparrow even more so. A successful pair of sparrows can have 5 clutches with 5 young in each clutch in a single summer season. Why are we not overrun by sparrows. Even Humans are in this category. A female human can have 10 babies in her lifetime and it wasn't so long ago that this was not unusual. Thank heaven for contraception. Without it, there would be standing room only. Actually, the result would be starvation and pestilence.

Most of the young of any animal you care to mention die and in fact, in a stable population, on average, only two young from each pair of adults survive to carry on the species and they themselves give rise to two survivors. Natural selection involves alot of death.

So how does this relate to animals living in an area of increased radiation. As long as the radiation isn't of such a level to "cook" any organism in the area, some offspring will be dealt a poor genetic hand, some not and natural selection will winnow out the ones with no aces. The winnowing will simply occur a little earlier in a population with higher radiation levels. In the case of our wolf, in a "normal" radiation area, all the pups could well survive during the summer with most of them starving in the winter if their food source is not sufficient*. In the high radiation area, it is likely that less of the litter will survive initially and by and large, the same number of wolves will survive into the next spring in both cases.

*Which will eventually occur at some point, if the wolf population is increasing.

Part of the reason we are so shocked is that if we humans were exposed to increased radiation, many of our children would be effected and we don't just shrug this off and let the maimed children die. In the animal world, without human interference, many young would die before they are born We never see this. Following hatching, many little sparrows fall. It may or may not meet his tender view but that is life (or rather natural selection). The radiation has to be pretty severe to cause an actual decrease in population. All animals produce a massive excess of young, surplus to what what is needed to keep the population in a steady state. As long as each pair leave more than two offspring who in turn produce more than two, the population grows.

This is clearly what has happened in Chernobyl. The radiation is not sufficient to kill off enough young to decrease the population. Quite the contrary. The animals have left more young than enough to grow the population

We get tied up in misunderstanding when we try to apply a human perspective of the acceptableness of having many wonky children to the Animal situation in which only a very few of the progeny of any animal survive even without increased radiation. Short of massive radiation levels, natural selection simply occurs a little earlier and as long as a few survive, the population will rise until it encounters the usual limiting factors, such as food supply at which point, the population will level out.

Note that in certain extreme areas with simplified assemblages of flora and fauna such as the Arctic, population boom and bust but still remain over all around the carrying capacity of their area.